分子筛用于丙炔/丙烯的高效分离

为解决传统的丙炔/丙烯分离能耗高,制约丙烯生产效率的问题,探讨了几种孔径尺寸接近的5A分子筛、4A分子筛和Silicalite 1分子筛对丙炔/丙烯的分离性能,通过吸附分离的方式,实现了高效的丙炔/丙烯分离。详细考察了5A分子筛、4A分子筛和Silicalite 1分子筛〖JP2〗在273 K和298 K下对丙炔/丙烯的单组分吸附性能,并进行了选择性计算。对5A分子筛、4A分子筛和Silicalite 1分子筛进行了模拟固定床的丙炔/丙烯(V〖DK〗(C3H4)∶V(C3H6)〖JP〗=1∶99)混合气穿透实验。结果表明,5A分子筛具有最优的分离效果。实现了基于分子筛对丙炔/丙烯的高效分离,为分子筛在低碳烃的分离应用提供了新的方向。     

A Single‐Molecule Propyne Trap: Highly Efficient Removal of Propyne from Propylene with Anion‐Pillared Ultramicroporous Materials

Propyne/propylene (C₃H₄/C₃H₆) separation is a critical process for the production of polymer‐grade C₃H₆. However, optimization of the structure of porous materials for the highly efficient removal of C₃H₄ from C₃H₆ remains challenging due to their similar structures and ultralow C₃H₄ concentration. Here, it is first reported that hybrid ultramicroporous materials with pillared inorganic anions (SiF₆^2? = SIFSIX, NbOF₅^2? = NbOFFIVE) can serve as highly selective C₃H₄ traps for the removal of trace C₃H₄ from C₃H₆. Especially, it is revealed that the pyrazine‐based ultramicroporous material with square grid structure for which the pore shape and functional site disposition can be varied in 0.1–0.5 Å scale to match both the shape and interacting sites of guest molecule is an interesting single‐molecule trap for C₃H₄ molecule. The pyrazine‐based single‐molecule trap enables extremely high C₃H₄ uptake under ultralow concentration (2.65 mmol g^?1 at 3000 ppm, one C₃H₄ per unit cell) and record selectivity over C₃H₆ at 298 K (>250). The single‐molecule binding mode for C₃H₄ within ultramicroporous material is validated by X‐ray diffraction experiments and modeling studies. The breakthrough experiments confirm that anion‐pillared ultramicroporous materials set new benchmarks for the removal of ultralow concentration C₃H₄ (1000 ppm on SIFSIX‐3‐Ni, and 10 000 ppm on SIFSIX‐2‐Cu‐i) from C₃H₆.     

用串联Al2O3/KCl柱分析1,3-丁二烯产品中痕量烃类杂质

为解决1,3-丁二烯中痕量烃类杂质丙炔等组分无法分离的问题,采用美国Agilent公司3种牌号大口径KCl型Al_2O_3柱,考察了1,3-丁二烯产品中痕量烃类杂质的分离情况,并建立了定量分析方法。结果表明:不同牌号Al_2O_3/KCl柱的分离效果差异较大,CP-Al_2O_3/KCl柱优于其他牌号;采用出峰顺序相同的2根Al_2O_3/KCl柱串联并优化色谱条件,能显著改善异戊烷、1,2-丁二烯、丙炔、正戊烷和1,3-丁二烯的分离,同时兼顾乙炔、丙二烯和异丁烷、正丁烷的良好分离,克服了Al_2O_3/KCl单柱无法满足关键组分基线分离的问题,同时满足痕量炔烃准确检测的需要。定量结果表明,各组分的检出限均低于2μg/g,相对标准偏差小于6.07%,加标回收率为84.5%～107.8%。     

Creating the hydrogen absorption capability of CeNi5 through the addition of Al

The hydrogenation capacities of CeNi_5?xAl_x (x = 0, 0.75, 1.0, 1.25, 1.5 and 1.75) alloys were assessed. In contrast to LaNi₅-based alloys, the addition of Al to CeNi₅ enables hydrogen absorption by creating larger interstitial sites as the result of an expanded lattice. Structure analyses indicate that each of these alloys maintained a CeNi₅ (CaCu₅-type) structure in which Al atoms exclusively occupied Ni 3g sites. Among these specimens, CeNi₄Al absorbed the greatest proportion of hydrogen atoms, decreasing its c/a ratio from 0.826 to 0.802 upon the formation of CeNi₄AlH_4.3. This drastic decrease in the c/a ratio is attributed to an anisotropic lattice expansion along the a-axis, as verified by in situ X-ray diffraction under H₂. The enhanced hydrogen absorption of these alloys is thought to be associated with the preferential situation of hydrogen atoms at interstitial sites located at the centers of octagons as well as a charge transition of Ce ions upon hydrogenation. It is verified that CeNi₄Al after hydrogenation shows high catalytic activity toward propyne hydrogenation: 100% conversion of propyne even at room temperature.     

Effects of synthesis conditions on the pervaporation properties of poly[1‐(trimethylsilyl)‐1‐propyne] useful for membrane bioreactors

An integrated fermentation and membrane‐based recovery (pervaporation) process has certain economical advantages in continuous conversion of biomass into alcohols. This article presents new pervaporation data obtained for poly[1‐(trimethylsilyl)‐1‐propyne] (PTMSP) samples synthesized in various conditions. Three different catalytic systems, TaCl₅/n‐BuLi, TaCl₅/Al(i‐Bu)₃, and NbCl₅ were used for synthesis of the polymers. It was found that the catalytic system has a significant influence over the properties of membranes made from PTMSP. Although a combination of a high permeation rate and a high ethanol–water separation factor (not less than 15) was provided by all PTMSP samples, the PTMSP samples synthesized with TaCl₅/n‐BuLi showed significant deterioration of membrane properties when acetic acid was present in the feed. In contrast, the PTMSP samples synthesized with TaCl₅/Al(i‐Bu)₃ or NbCl₅ showed stable performance in the presence of acetic acid. When using a multicomponent mixture of organics and water, the copermeation of different organic components results in lower separation factor for both ethanol and butanol. These data are consistent with nanoporous morphology of PTMSP. It was demonstrated that pervaporative removal of ethanol improved the overall performance of the fermentation process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2271–2277, 2004     

A small detailed chemical-kinetic mechanism for hydrocarbon combustion

A chemical-kinetic mechanism is presented that is designed to be used for autoignition, deflagrations, detonations, and diffusion flames of a number of different fuels. To keep the mechanism small, attention is restricted to pressures below about 100 atm, temperatures above about 1000 K, and equivalence ratios less than about 3 for the premixed systems, thereby excluding soot formation and low-temperature fuel-peroxide chemistry. Under these restrictions, hydrogen combustion is included with 21 steps among 8 chemical species, combustion of carbon monoxide with 30 steps among 11 species, methane, methanol, ethane, ethylene, and acetylene combustion with 134 steps among 30 species, and propane, propene, allene, and propyne combustion with 177 steps among 37 species. The mechanism has been extensively tested previously for all of these fuels except propane, propene, allene, and propyne. Tests are reported here for these last four fuels through comparisons with experiments and with predictions of other mechanisms for deflagration velocities and shock-tube ignition.     

乙烯装置C3加氢系统存在问题的分析及改造

针对１６万ｔ／ａ乙烯装置存在催化剂活性低、使用周期短的问题,对系统进行了技术改造。通过优化Ｃ３加氢条件,延长Ｃ３加氢反应器的再生周期,降低Ｃ３加氢后丙炔和丙二烯含量,从而使丙烷成为合格的裂解原料。     

Positron annihilation lifetime studies of gas sorption and desorption in polyethylene and poly[1‐(trimethylsilyl)‐1‐propyne]

The variation of free‐volume parameters (lifetime, intensity, and distribution) after sorption and desorption of CO₂ and CH₄ gases in the glassy polymer poly[1‐(trimethylsilyl)‐1‐propyne] (PTMSP) and in the rubbery high‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) were determined by the PAL technique. Size distributions deduced from PAL measurements reveal the presence of large free‐volume holes in PTMSP with an average size of 0.725 nm³ and intensity of 22% in addition to a free‐volume hole size of 0.197 nm³ with an intensity of 11%. In polyethylene free‐volume hole sizes of 0.107 and 0.153 nm³ with intensities of 21% and 25% could be deduced for HDPE and LDPE, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 970–974, 2001